1. Field of the Invention
The present invention relates to a sheet conveying apparatus for conveying a recording sheet in a printer, typewriter, copying machine and the like and a conveying apparatus for conveying an original to be read in a facsimile system, a copying machine, image reader, OCR and the like, and more particularly, it relates to a sheet conveying apparatus useful for systems wherein a sheet being conveyed should not be floating at a desired position.
2. Related Background Art
In the past, sheet conveying apparatuses used with a printer, scanner and the like are mainly of the type wherein pinch rollers are urged against a convey roller comprising a high friction surface member so that a sheet pinched between the convey roller and the pinch rollers is conveyed by friction forces generated between the rollers. According to one aspect, each pinch roller is mounted on a corresponding pinch roller holder made of plastic material and is biased toward a convey roller by a spring and the like.
In the conventional sheet conveying apparatuses, it is necessary to provide one pinch roller holder for each pinch roller, and, since any gap must be maintained between the adjacent pinch roller holders, it is very difficult to urge the whole sheet against the convey roller uniformly. Thus, in an apparatus wherein a sheet being conveyed should not be floating at a desired position, there arises a problem if the sheet cannot be uniformly urged against the convey roller. Particularly, in an ink jet printer, since the sheet gets wet due to the ink discharged from a recording head, a recording surface of the sheet is floating, thereby deteriorating the recording quality.
To avoid this, a plurality of pinch rollers may be mounted on a single pinch roller holder. In this case, however, if the single pinch roller holder is distorted or twisted, there arises the dispersion in the urging forces of the pinch rollers, thus causing a problem that gaps are created between some pinch rollers and the convey roller.
The recording apparatuses can be grouped into ink jet type, wire dot type, thermal type, electrophotographic type or the like on the basis of the recording modes. The recording apparatus of ink jet type has many advantages that it has low noise, low running cost, low apparatus cost, high speed recording ability and compact body. Further, generally, since the recording head is not contacted with the recording sheet, by maintaining a small and constant gap between the recording head and the recording sheet, it is possible to obtain the high image quality. To this end, the recording .sheet is held down by pinch rollers arranged near the recording head. In this case, since the recording sheet is held down in the proximity of the recording head, diameters of the pinch rollers are made smaller.
However, when the conveyance of the recording sheet and the registration of the recording sheet are effected by using the small pinch rollers and the convey roller, since a nip between each pinch roller and the convey roller is small, if a thick sheet such as a post card is handled, the sheet cannot be adequately pinched between the nips, thereby causing the poor protruded amount and the poor registration.